I ended up deleting the entry, and it's just using whatever size the images are.
I think on post.php there is a similar setting, because right below the bold/italic/underline/link options are all the smilies, and they're all shrunk down to the same size.
Is there a way to change that?
I was thinking it might be here, but I'm not sure:
$forum_page['text_options']['smilies'] = '<span'.(empty($forum_page['text_options']) ? ' class="first-item"' : '').'><a class="exthelp" href="'.forum_link($forum_url['help'], 'smilies').'" title="'.sprintf($lang_common['Help page'], $lang_common['Smilies']).'">'.$lang_common['Smilies'].'</a></span>';
// Setup breadcrumbs
$forum_page['crumbs'][] = array($forum_config['o_board_title'], forum_link($forum_url['index']));
$forum_page['crumbs'][] = array($cur_posting['forum_name'], forum_link($forum_url['forum'], array($cur_posting['id'], sef_friendly($cur_posting['forum_name']))));
if ($tid)
$forum_page['crumbs'][] = array($cur_posting['subject'], forum_link($forum_url['topic'], array($tid, sef_friendly($cur_posting['subject']))));
$forum_page['crumbs'][] = $tid ? $lang_post['Post reply'] : $lang_post['Post new topic'];